This invention relates generally to irrigation sprinklers of the type having a spray head rotatably driven in steps through a full-circle or selected part-circle arcuate path. More particularly, this invention relates to a rotary drive sprinkler having improved rotary drive means for indexing the spray head at a substantially constant stepping rate irrespective of water pressure supplied to the sprinkler, and wherein the drive means is designed for reliable long-term operation without accumulation of grit and the like.
A variety of rotating spray head sprinklers are well known in the irrigation art and typically include a sprinkler housing with a rotatable spray head adapted for connection to a supply of water under pressure. The spray head includes a nozzle oriented for outward passage of a stream of water under pressure normally in an upwardly angled and laterally outward direction for irrigation of a surrounding terrain area. A suitable drive means is provided for rotating the spray head through a full-circle rotational path or reversibly between adjustable end limits of a part-circle arcuate path, frequently in stepwise increments to change the azimuthal direction of the projected water stream.
In many rotating water sprinklers, it has been desirable to mount the rotary drive means in a protected position encased within the sprinkler housing to minimize contact with environmental elements and conditions, such as sand, grit, wind, and the like. Such sprinklers have commonly included rotary water-driven turbines or the like for indexing the spray head via a reduction drive gear train. In some of these sprinklers, ball-drive mechanisms or other intermittent motion devices are used to provide stepwise driving of the spray head. See, for example, the rotary drive sprinklers depicted in U.S. Pat. Nos. 3,930,618, 4,026,471, 4,253,608, and 4,417,691.
One disadvantage encountered with rotating water sprinklers of the above-described general type, however, is that the rotary driving or stepping speed as well as the magnitude of each rotational increment tend to be direct functions of water pressure supplied to the sprinkler. This functional relationship can result in significant variations in the application of irrigation water by a plurality of sprinklers within a common irrigation system due, for example, to water pressure variations incidental to terrain elevational differences and the like. Moreover, when the water pressure is relatively high, the sprinklers can experience relatively high rotational driving speeds which can cause significant internal wear of moving parts and thereby increase requirements for mechanical repair and replacement. Still further, over time, rotary drive sprinklers with internally-mounted drive mechanisms are subject to clogging by accumulating water-entrained grit and the like, resulting in operational failures.
There exists, therefore, a significant need for an improved rotary drive sprinkler of the type having rotary drive means protectively encased within a sprinkler housing, wherein the rotary drive means is adapted for substantially constant rate spray head stepping motion irrespective of water supply pressure and wherein the drive means is substantially unaffected by dirt or grit within the water supply. The present invention fulfills these needs and provides further related advantages.